1. Field of the Invention
This invention relates to insulated electrical wire and cable useful in nuclear generating stations, as well as in other applications.
2. Description of the Prior Art
Electrical wire and cable suitable for use in nuclear power generating stations must be designed to withstand extremely severe conditions. Such wire and cable, referred to hereafter simply as cable, are useful for power, control and instrumentation services provided in proximity to, but not within, the reactor vessel. The extreme conditions which such cable must withstand include normal conditions as well as extraordinary conditions, such as accidents and the like. Under normal conditions, the cable must be suitable for operation at reactor full-load ambient temperature, radiation and atmospheric conditions and normal electrical and physical stresses for its installed life. Extraordinary conditions are known as design basis events (DBE), which are postulated abnormal events employed in the design of the reactor to establish the performance requirements of structures and systems, and include loss-of-coolant accident (LOCA) and fires. The cable must be capable, either early or late in its normal design life, of operating through postulated environmental conditions, including wet and radiation environments, resulting from LOCA. Conditions of loading and signal levels during LOCA testing are assumed to be those most unfavorable for cable operation which may be anticipated under such circumstances. In addition, the cable should be fire retardant with respect to propagation under conditions of installation. Performance during a fire is related to those conditions which would extend the influence of the fire to cables of redundant systems.
It is critical that cable intended for so-called Class IE electrical equipment (that is, equipment that is essential to the safe shut-down and isolation of the reactor or whose failure or damage could result in significant release of radioactive material) withstand the operating conditions mentioned above. To be useful in such installation, the cable should meet standards generated by the Institute of Electrical and Electronics Engineers, known as IEEE Standard 383. Heretofore, it has been suggested that in view of their excellent chemical resistance and electrical properties, the fluoropolymer resins, such as a copolymer of ethylene and chlorotrifluoroethylene be employed as insulation for nuclear power cables. However, it has been found that cables provided with ethylene-chlorotrifluoroethylene copolymer primary insulation do not meet the rigid LOCA requirements of IEEE Standard 383 when tested at 600 volts for use as power or control cables, although they do meet such requirements when tested at 300 volts.